Distribution of eggs and larvae of Japanese anchovy Engraulis japonicus in the Pacific waters off northern Japan in summer

Abstract

Coincident with the population increase in the 1990s, egg and larva distributional area of the Pacific stock of Japanese anchovy Engraulisjaponicus expanded from the warm Kuroshio waters toward the cold Oyashio waters off northern Japan. To understand how Japanese anchovy expanded its spawning and nursery grounds, egg and larva distributions and larval growth rates were investigated in relation to temperature and flow fields in the Pacific waters off northern Japan (Pacific North, PN) in summer. Anchovy eggs occurred in the Oyashio waters (≤5 °C at a 100-m depth) warmer than or equal to 15.9 °C in sea surface temperature (SST) which is close to the known lower limit of spawning temperature. Eggs and larvae would be transported southwestward to the warmer coastal and offshore waters by the currents dominated in the study area. Temperature experienced by anchovy eggs and larvae in the northern subarctic waters was almost the same as that in the southern spawning ground in spring. Larval growth rates in the study area were comparable to the previous studies in the southern nursery areas. Thus, the subarctic PN waters would function as spawning and nursery grounds of E. japonicus in the decades of high stock abundance.